This invention relates to a stabilizer composition for polymer materials, particularly for polyolefines. The stabilizer composition comprises alkylated aralkylphenol and bis (aralkylphenyl) pentaerythritoldiphosphite.
The need for protection of polymer materials against thermooxidation degradation during their processing, storage and utilization has been increasing due to various factors. More particularly the mechanical and thermal strain, UV radiation, air oxygen and the like, cause the scission of polymer chains and the subsequent oxidation of fragements thus formed. Moreover, upon melting, a change of physico-mechanical properties of the polymer material results.
It is presently known that sterically hindered phenols and phosphites are generally employed as stabilizers for polyolefins. Among the known phenols, 2,6-di-tert-butyl-4-methylphenol and 2-tert.-butyl-4-(alpha-dimethylbenzyl) phenol (CS 235 169) show high efficiency during the processing of the polymer, but they are relatively volatile at higher processing temperatures, and thus the efficiency during utilization decreases. High-molecular phenolic antioxidants, at the same level of dosage are less efficient. Both groups can result in the undesirable coloring of the polymer.
Phosphite stabilizers offer relatively good processing stability and thermooxidation stability. However, they are subject to considerable hydrolyzation and problems associated with it during storage and processing with the result that their use is less advantageous. Low-molecular type phosphites are liquid which result in yellowing during their service. Higher-molecular pentaerythritol phosphites described in CS 191 331 and CS 211 116, eliminate these deficiencies but increase the cost for the stabilization system.
It is a well known fact that in some cases during the combination of various types of stabilizers there is a mutual interaction of respective components of such a stabilization system. Accordingly, a great deal of research is directed to the synergistic effect as the basis for the decrease of the cost for the stabilization and extension of the service life of goods made of plastics during their utilization. In U.S. Pat. No. 3,535,249 there is described the antioxidation mixture comprising the phenolic antioxidant, deactivator of the action of heavy metals and reduction agent, for polyolefines. Vulcanizates made of unsaturated rubbers can be protected by the synergistic combination of 2-mercaptobenzimidazole with the phenolic or amine antioxidant (CS 165 480, CS 244 977).
There are well known multi-component systems based on phenolic and phosphite antioxidants conceivably with other co-stabilizers. For example, the GB Patent No. 1,526,603 is drawn to the process of the preparation and application of bis (dialkylphenyl) pentaerythritoldiphosphite together with phenolic antioxidants. Other patents, JP No. 0 250 031, JP No. 155 486, JP No.255 229, CS No. 190 837 and EP No. 184 191 are drawn to multi-compositional systems, comprising phenolic and phosphite stabilizers.